1. Field of the Invention
This invention relates to a two-stroke cycle internal combustion engine designed for crankcase scavenging and comprising an exhaust passage which extends from an exhaust port in the cylinder wall and which contains a control member, which is adjustable in the direction of travel of the piston to adjust the flow area of the exhaust port in dependence on one or more operational parameters of the internal combustion engine, in particular, in dependence on its speed.
2. Description of the Prior Art
Two-stroke cycle internal combustion engines of that kind are already known, e.g., from British Patent Specification 2,177,755, U.S. Pat. Nos. 4,516,530, and 4,768,473. But in those known engines the control member is so arranged and designed that it is operable to adjust that edge of the exhaust port which is remote from the crankshaft in order to prolong or shorten the exhaust time in dependence on speed in adaptation on the operating conditions. From British Patent Specification 2,177,755 it is also known to provide two lateral exhaust passages in addition to a main exhaust passage and also to provide an air chamber, which is closed to the outside and adapted to be connected to the exhaust system. In that case the control member serves also for selectively closing the lateral exhaust passages and the air chamber so that the opening period of the main exhaust passage and of the lateral exhaust passages can be reduced during an operation at low speed whereas during an operation at high speed the flow areas of the exhaust passages can be entirely opened and the air chamber can be closed in order to increase the power of the engine. But the scavenging losses cannot be decreased by such measures.
In internal combustion engines in which the pollutant content of the exhaust gas is minimized and in which exhaust systems comprising a catalytic converter can be used, it is essential to minimize the emission of pollutants from the internal combustion engine. For this reason the scavenging losses should be minimized and the internal combustion engine is desired to combust even very lean mixtures while having a good driveability.